Geochemical and isotopic characteristics of volcanic rocks from the northern East China Sea shelf margin and the Okinawa Trough

Abstract

Volcanic rocks both from the northern East China Sea (NECS) shelf margin and the northern Okinawa Trough are subalkaline less aluminous, and lower in High Field Strength Elements (HFSE). These rocks are higher in Large Ion Lithophile Elements (LILE), thorium and uranium contents, positive lead anomalies, negative Nb-Ta anomalies, and enrichment in Light Rare Earth Elements (LREE). Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt (MORB), and rhyolites from the northern Okinawa Trough have the highest 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios. The NECS shelf margin basalts have lower 87 Sr/ 86 Sr ratios, ε Nd and σ 18 O than the northern Okinawa Trough silicic rocks. According to 40 K-40 Ar isotopic ages of basalts from the NECS shelf margin, rifting of the Okinawa Trough may have been active since at least 3.65-3.86 Ma. The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere. The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough, and the formation of basaltic magmas closely relates to the thinning of continental crust. The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough, which could have been generated by the interaction of basaltic melt with an enriched crustal component. From the Ryukyu island arc to East China, the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements (HREE), suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate, and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.

Petrology and mineralogy of pumice from the Iheya North Knoll, Okinawa Trough: Implications for the differentiation of crystal‐poor and volatile‐rich melts in the magma chamber

“…Felsic volcanic rocks have been found in all three parts of the OT (e.g., Chung, Wang, Shinjo, Lee, & Chen, 2000;Shinjo & Kato, 2000;Zeng et al, 2010). Basalts have been uncovered in some central grabens in the MOT (Shinjo & Kato, 2000;Zhao, Luo, Lai, Tian, & Xu, 2016) and the SOT (Shinjo et al, 1999).…”

Actively forming Kuroko-type volcanic-hosted massive sulfide (VHMS) mineralization at Iheya North, Okinawa Trough, Japan

“…1a). A rift-related bimodal basaltic-rhyolitic suite, accompanied by minor intermediate rocks, characterizes the middle Okinawa Trough (Ishizuka et al, 1990;Shinjo et al, 1999;Shinjo and Kato, 2000;Zeng et al, 2010). Thick (~1000 m) sequences of organic-rich terrigenous sediments sourced from the Yangtze and Yellow rivers overlie basement lithologies .…”

Petrogenesis of basalt from the middle Okinawa Trough: New insights from olivine‐hosted melt inclusions

“…The volcanic rocks in the MOT exhibit bimodal characteristics, forming a basaltic-rhyolitic suite (Li et al, 1997). The volcanic rocks in the central grabens in the MOT and SOT are younger than 1 Ma (Ishikawa et al, 1991;Shinjo, Chung, Kato, & Kimura, 1999;Zeng et al, 2010). The volcanic rocks in the central grabens in the MOT and SOT are younger than 1 Ma (Ishikawa et al, 1991;Shinjo, Chung, Kato, & Kimura, 1999;Zeng et al, 2010).…”

“…Since the 1980s, many investigations of the OT have been conducted (Lee, Shor, Bibee, Lu, & Hilde, 1980;Letouzey & Kimura, 1985), and considerable geophysical and geological data have been generated. However, its tectonic and petrological aspects have received less attention (Yan & Shi, 2014), resulting in many controversies regarding the types of mantle sources and the magma evolution (e.g., Guo, Zhai, Yu, Cai, & Zhang, 2016;Guo, Zhai, Yu, Wang, et al, 2016;Huang, Li, & Jiang, 2006;Ishizuka, Kawanobe, & Sakai, 1990;Liao, Huang, & Hu, 2016;Shinjo, 1999;Yu, Zhai, Guo, Zhou, & Zong, 2016;Zeng et al, 2010;Zhai et al, 2017). Volcanic rocks can provide important information regarding the tectonic activity and geodynamic mechanisms in the OT.…”

“…Huang et al (2006) researched the Sr and Nd isotopes of volcanic rocks in the northern OT (NOT) and MOT and found that magma material in the OT is derived from a PREMA mantle source. Zeng et al (2010) considered that the basalt in the NOT was produced by the interaction between Indian Ocean-type mantle and continental lithosphere. Zeng et al (2010) considered that the basalt in the NOT was produced by the interaction between Indian Ocean-type mantle and continental lithosphere.…”